This invention relates generally to bicycle stem assemblies, and, more particularly, to a welded, single bolt stem assembly for connecting the handlebars to the front fork of a bicycle frame.
There are a variety of stem assemblies for securing the handlebars of a bicycle to the front fork of a bicycle frame. In bicycles intended for easy use primarily over smooth surfaces such as sidewalks or roadways, single bolt stem assemblies may be used. These single bolt stems are characterized by a single bolt being used to both clamp the handlebar to the stem and to clamp the stem to the fork of a bicycle frame. Single bolt stem assemblies generally include a tubular barrel adapted to mount to the front fork of the bicycle frame and a handlebar clamping head which is connected to the barrel. The handlebar clamping head of known single bolt stems is formed with a top portion, a bottom portion, and a connection portion which is bent into a U-shaped configuration adapted to receive and clamp the handlebars.
In order to mount the handlebar clamping head of prior art single bolt stem assemblies to the tubular barrel, a relatively large bore was characteristically formed in the bottom portion of the head. The top end of the tubular barrel was extended through the bore in the bottom portion of the head and the upper portion of the head extended over the top end of the barrel. In some prior art designs, the handlebar clamping head was welded to the barrel by a circular weld extending around the barrel and interconnecting the bottom portion of the head with the barrel, such as shown in German Pat. No. 2,717,316. In other prior art designs, the bottom portion of the handlebar clamping head seated on a shoulder formed on the barrel, such as shown in French Patent No. 568,501. In either design, a mounting bolt was inserted through a bore formed in the upper portion of the head, through the barrel, and into threaded engagement with a wedge nut adapted to secure the barrel to the front fork of a bicycle frame. The bolt functioned both to urge the upper portion of the head toward the lower portion, thereby clamping the handlebar in the U-shaped intermediate portion of the head, and to pull the wedge nut upwardly relative to the barrel and thereby clamp the stem to the fork of a bicycle frame.
Prior art single bolt stem assemblies are advantageously used in bicycles which are relatively inexpensive or in bicycles which are exclusively intended for roadways or other smooth surfaces. Single bolt stem assemblies are inexpensive to manufacture compared to multiple bolt stem assemblies, because they are made of less material and are simpler to fabricate. However, a significant problem associated with both of the single bolt designs described above is that in order to form the bore in the bottom portion of the head so that it can be placed over the barrel for mounting the head to the barrel, a substantial amount of metal must be removed to form the bore. It has been found that failures often occur in the bottom portion of the head in the area of the bore due to cracking of the relatively thin sections of metal adjacent the bore when the clamping head is tightened about the handlebars and/or when weight is applied to the handlebars during use of the bicycle.